【作者】 潘建；

【导师】 朱德庆； John Clout；

【作者基本信息】 中南大学 ， 钢铁冶金， 2007， 博士

【摘要】 钢铁工业是能耗大户，也是污染大户，而烧结工序是钢铁工业中排放空气污染物的主要污染源之一，由烧结工序产生的SO₂约占钢铁生产系统空气污染物中SO₂的40％～60％，烧结能耗则占钢铁工业总能耗的10％～15％。目前，国外发达国家对钢铁工业中SO₂、NO_x等的治理技术已经商业化，进入第三代污染物CO₂以及二嗯英等治理技术的研究和应用阶段。国内则由于技术和经济方面的原因，对钢铁工业的SO₂、NO_x的污染控制尚处于工业化应用前期研究，而烧结烟气脱硫脱硝处理基本处于空白，CO_x排放量的控制更没纳入议事日程。本论文结合国家自然科学基金项目《烧结烟气SO₂、NO_x、CO₂减量化排放基础理论与应用研究》（NSFC50274072），从清洁生产的观点出发，通过热重分析、红外光谱测试、X-射线衍射分析、扫描电镜及能谱分析、气相色谱分析等分析测试技术及对烧结烟气中SO_x、NO_x、CO_x在线检测等手段，对铁矿烧结工艺过程SO₂、NO_x、CO_x烟气的形成机制、排放规律及影响因素进行了研究。系统研究了铁矿烧结烟气中SO₂生成机理，结果表明：铁矿烧结烟气中SO₂来源于含铁原料和燃料中硫在高温下的热解，烧结混合料中硫的热解和脱硫率主要受温度、时间、空气中氧浓度、焦粉粒度等因素的影响。烧结脱硫率越高，烧结矿中残余的硫含量越低，越有利于改善生铁质量，但烧结烟气中排放的SO₂量越大。研究表明，脱硫率随温度升高、加热时间延长、氧浓度提高和焦粉粒度减小而迅速升高。但温度过高，烧结混合料中硫的脱除率愈低，烟气中SO₂排放量愈少。首次揭示了烧结烟气中SO₂的排放特征，提出了烧结烟气中SO₂浓度变化具有自持性的新观点，即无论烧结工艺参数和原料特性如何变化，烧结烟气中SO₂浓度始终在烧结终点前某一时刻急剧上升到最大值，随后急剧下降。阐明了烟气中SO₂的排放特征受烧结料层水分的迁移规律及料层中SO₂的热解生成-吸附-解吸机制所控制。采用动态法研究了烧结混合料对SO₂的吸附机理和吸附动力学，结果表明，在低吸附量时吸附速度1/C（?） dA/dt与吸附量A遵从一级反应动力学方程，两者有较好的线性关系；并且在吸附初期，当混合料碱度越高且CaO来源于生石灰、混合料含水量高、混合料平均粒度细及烟气中SO₂浓度越高时，均有利于混合料对烟气中SO₂的多相反应吸附过程。随着料层对SO₂的吸附量增加，吸附速度与吸附量间符合零级反应，吸附速度不再随吸附量的增大而加快。研究SO₂在烧结料层中的迁移规律时发现，存在CaSO₃的再氧化和CaSO₄的高温热分解过程，这是导致烟气中SO₂排放存在峰值特征的主要原因之一。在此理论研究基础上，创立了烧结过程SO₂的热解生成-料层吸收-热解解吸的迁移及富集排放模型，成功开发出了烧结烟气分段脱硫新工艺。在采用湿法石灰石-石膏法脱硫工艺的前提下，与传统全烟气脱硫相比，分段烟气脱硫新工艺减少烟气处理量40％，烟气脱硫率提高2．4％，吸收液大幅度减少，烟气脱硫设备投资和运行成本可明显降低。在线检测烧结烟气的气体成分表明，铁矿烧结烟气中NO_x主要来源于烧结点火阶段煤气燃烧及烧结料层中固体燃料燃烧。烧结过程生成的NO_x也主要以NO为主，只有微量的NO₂存在。与烧结过程烟气中SO₂的排放规律相比，烧结过程烟气中NO_x的排放存在显著差异，从点火结束后开始到烧结终点前，始终保持在一个较高的浓度水平。NO_x的生成及排放量受燃料N含量、氮的存在形态、燃料粒度、空气中氧含量、烧结混合料化学成分等因素的影响。而研究结果表明，提高烧结碱度或增加烧结料层高度均有利于降低烟气中NO_x排放浓度，由此提出了烧结过程形成的铁酸钙对烧结体系的NO_x还原反应具有催化作用。根据铁矿烧结特点，运用晶体结构、反应活化能、催化还原反应的热力学和动力学基础理论，系统研究了铁酸钙自催化NO_x还原反应机理。研究表明，烧结料层中的铁酸钙对CO还原NO反应具有明显的自催化作用。催化作用的强弱取决于铁酸钙的结构特点，其催化能力由强到弱的顺序为CF>C2F>2CF，CF使CO还原NO反应的活化能由无CF存在时的246．68 kJ／mol降到有CF存在时的138．80kJ／mol；揭示了铁酸钙催化CO还原NO的反应机理为：作为催化剂的铁酸钙参与了反应，发生了催化剂被CO还原和被NO重新氧化的反应，与此同时，铁酸钙催化NO还原还服从多相催化的吸附活化物理论，在铁酸钙催化剂活性部位发生NO分子吸附、离解、表面活性物种的重组和产物脱附的反应。在铁酸钙自催化作用下，降低了烧结体系NO还原的表观反应活化能，加快了反应速度。促进铁酸钙在烧结矿表层的分布和提高烧结矿中铁酸钙矿物的含量，有利于强化铁酸钙自催化作用和降低NO_x的排放，在此基础上开发了分流制粒非均质烧结新工艺，优先发展铁酸钙系粘结相，改善铁酸钙在烧结矿表层的分布，与常规烧结工艺流程相比，可降低NO_x排放浓度44％左右。对烧结过程固体燃料的燃烧特性进行了系统研究，运用催化燃烧和燃烧化学的理论，成功开发出具有助燃和助熔多种功能的烧结节能添加剂，改善了烧结矿产质量指标，降低烧结固体燃耗，烧结过程CO、CO₂和NO_x的排放浓度也明显降低，但烧结料层中氧化性气氛增强，强化了烧结混合料中硫的脱除，烧结烟气中SO₂的排放浓度峰值有所提高，但其排放规律仍维持其自持性。研究表明，节能添加剂催化焦粉燃烧的作用机理为活化固定碳的晶体结构、形成反应活性中心、降低反应活化能和促进燃烧过程的氧传递，焦粉经节能添加剂处理后，气化反应活化能由25．8kJ／mol降低到18．9kJ／mol，燃烬率由80．2％提高到89．8％，燃烧速率由2．25％／min加快到3．15％／min；催化剂中还含有助熔剂，可诱导低熔点的铁酸钙液相形成，在较低烧结温度下使液相产生的速度加快，粘结相量增多，从而提高烧结成品率和烧结矿强度。烧结节能添加剂工业试验结果进一步证明，烧结产质量指标明显改善，产量提高了15．72％，转鼓强度提高了1．99％，固体燃耗降低了4．19 kg·t_烧结矿^-1，烧结过程废气中CO₂浓度下降10．53％，CO浓度降低35．29％，NO浓度降低25％，但SO₂平均排放浓度提高了16．74%，峰值排放浓度提高了17．70％，还需结合后续烟气处理才能达到烧结烟气SO₂的减量排放。通过对铁矿烧结过程SO₂、NO,、CO_x排放规律的系统研究，设计了烧结烟气减量排放综合方案，即有机结合烟气分段处理+烧结节能添加剂+热风返烟烧结的工艺方案。以450m²烧结机为例，与传统工艺流程相比，综合方案可减少烧结烟气脱硫时40%左右的处理烟气量，烧结烟气脱硫装置设备投资和运行成本分别可减少40％左右，而由热风返烟烧结节约的固体燃耗可带来直接经济效益936万元。更多还原

【Abstract】 The iron and steel industry consumes more energy and brings about heavier pollutions than other ones,especially sinter mills are one of the main emissions of air pollutants in integrated steelworks, with SO₂ emissions accounting for 40%-60% of the total.At the same time the unit energy consumption amounts to about 10%-15% of total energy consumption of steelworks. At present, the techniques reducing the emissions of SO₂ and NO_x from iron and steel industry has been put into operation commercially in some developed country, even the efforts to minimize the emissions of CO₂ and polychlorinated dibenzo-p-dioxins and -furans （PCDD/F） have also been made. However, the control techniques of air pollutants such as SO₂ and NO_x are still on the prophase of industrialization in iron and steel industry of China because of the deficiency of techniques and economy.For sinter plants,the desulphuriza-tion and denitrification of flue gas has not been applied except for few small sinter strands, the minimisation of CO₂ emissions were even not brought into schedule.Theoretical and process studies of the abatement of CO₂,NO_x and SO₂ during iron ore sintering was conducted,which was supported by National Natural Science Foundation of China（NSFC50274072）. Based on the viewpoint of clean production, the formation mechanism, the emissions and the factors affecting the formation and emissions of SO₂, NO_x, CO₂ during iron ore sintering were studied systematically via different measures for the first time,such as TGA, infrared spectral analysis,XRD analysis, SEM analysis, gas chromatography and online analysis.The formation mechanism of SO₂ during iron ore sintering was fully studied, the results show that sulphur oxides （mainly SO₂） in the flue gas originate from the pyrogenation of sulphur compounds in the iron ore and coke breeze at high temperatures.The pyrogenation of sulphur and the rate of desulfurization were mainly affected by these factors, such as temperature, time, oxygen concentration and coke particle size. With an increase in desulfurization,the remnants sulfur contents of sinter are further reduced improving the quality of pig iron. However, the emissions and concentration of SO₂ in the flue gas increase significantly. And the desulfurization augments rapidly along with the temperature, calefaction time,oxygen concentration and a decrease in the coke particle size. However,too higher temperature would deteriorate the desulfurization and lead to a lower emission of SO₂. In this paper, it is put forward means that the emission of SO₂ possesses the characteristics of self-sustaining which means the emission of SO₂ rises to a peak value rapidly just before the sintering end point and declines dramatically no matter how parameters of sinter technology and the properties of raw material change. It is also revealed that the emission of SO₂ is controlled by the transfering pattern of moisture in sintering bed,and also controlled by the mechanism of pyrogenation formation-adsorption-desorption of SO₂. The adsorption mechanism and kinetics of sinter bed adsorbing SO₂ were studied by adopting dynamic methods.It is shown that the relationship betweenadsorptive rate 1/C_o dA/dt and adsorption capacity A agrees linely with the first order reaction kinetics equation at low adsorption capacity. Furthermore, at the initial stages of adsorbing, the multiphase reaction of blends absorbing SO₂ is enhanced by an increase in the basicity of blends, with CaO originating from quicklime better than limestone, the moisture of blends and the concentration of SO₂ in the flue gas, and decrease in the average particle size of blends, raising. With the adsorption capacity increasing sequentially, the relationship between adsorptive rate and adsorption capacity would obey zero order reaction kinetics equation, with the adsorptive rate at steady state.During the transfering of SO₂ in sinter bed, there occur important reactions,such as the oxidization of CaSO₃ and thermal decomposition of CaSO₄ at high temperatures, which dominates the self-sustaining characteristics of the emission of SO₂. Based on the theoretical research,an emission model describing the pyrogenation formation-adsorption-desorption reactions of SO₂ in sintering bed was founded innovatively, and a new technology of sectional desulphurization of flue gas was developed triumphantly. When the limestone-gypsum wet flue gas desulfurization technology used in a sinter plant ,compared with conventional desulphurization tecnology, the new technology of sectional desulphurization can reduce the volume of flue gas by about 40% to be treated, resulting in the lower consumption of absorbing solution, an increase in desulfurization by about 2.4%, Moreover the investment of waste gas treatment facilities and operational costs can be significantly decreased.The results of online measurement of sinter flue gas showed that NO_x emitting from sintering flue gas originates primarily from the combustion of gas fuel during ignition and solid fuel in sintering bed. Fuel NO_x is the main resource while prompt-NO_x and thermal-NO_x are inferior. Furthermore, NO dominates and NO₂ only amounts to several ppm among NO_x. Compared with the emission of SO₂ during sintering, the emission of NO_x is quite different. From the finish of ignition to the end of sintering, the concentration of NO_x in the flue gas always maintaines at a high level.The amount of NO_x generated was affected by some factors, such as the fuel-N content, the presence form of nitrogen, the particle size of fuel, the oxygen content in the air,the material composition of sinter blends.It is shown that an increaseing in basicity of sinter and sinter beds height are conducive to reducing the emission of NO_x in flue gas.It is inferred that calcium ferrite（CF） forming during sintering catalyzes the reduction of NO_x.Based on the characteristics of iron ore sintering,and using the theories of crystal structure, activation energy, the thermo-dynamic and kinetics of catalytic reduction, the mechanism of calcium ferrite catalyzing NO_x reduction was studied. It is demonstrated that calcium ferrite catalyzes the reduction of NO by CO, and the catalytic capacity of calcium ferrite depends on their molecular structure.The order of catalytic capacity from strong to weak is as following: CF> C2F>2CF. Compared with the reduction of NO by CO with absence of CF, the activation energy is declined from 246.68 kJ /mol to 138.80kJ /mol when CF occurs during the reduction of NO by CO. The mechanism of calcium ferrite catalyzing NO_x reduction is proven for the first time. During the reaction course, calcium ferrite is reduced by CO and oxidized by NO. The mechanism of calcium ferrite catalysing NO_x reduction also obey the theoretics of adsorption-activation where NO molecule adsorbs, decomposes,surfactant species restructures and product desorbs at activity site of calcium ferrite catalyst.The function of calcium ferrite catalysing NO_x reduction is defined as self-catalysis in sintering system,where CF reduces the activation energy and accelerate the reaction rate. It is the self-catalysis of calcium ferrite help to abate NO_x emission by improving the calcium ferrite distribution on the surface of sinter bed and increasing the calcium ferrite proportion in sinter.Therefore, a new technology of separate granulation and heterogeneous sintering （SGHS）was put forward, which can develop calcium ferrite firstly and modify the calcium ferrite distribution on the surface of sinter. Compared with the traditional sintering process, the emission of NO is nearly reduced by 44% ,and sinter quality is also improved by the new SGHS process.On the basis of study of the combustion of solid fuel in sintering process and using the theories of catalytic combustion and combustion chemistry, an energy-saving additive with multiple functions, such as improving combustion and reducing fusion temperature, was developed successfiilly,which improves the quality and productivity of sinter, decreases solid fuel consumption, and lower the emissions of CO, CO₂ and NO_x significantly. Due to an enhancement in the oxidizing atmosphere of sinter beds, the desulfurization of sinter blends is strengthened, with a higher peak value of SO₂ concentration occurring in the flue gas. However, the characteristics of self-sustaining is not affected. It is shown that action mechanism of the additive catalysing coke combustion is by activating the crystal structure of fixed carbon and forming reaction centers, the activation energy is decreased and the oxygen transfer is promoted in the combustion process.When coke is soaked by the solution of sintering energy-saving additive,the gasification activation energy of coke was decreased from 25.8kJ/mol to 18.9kJ/mol, combustion efficiency was increased from 80.2% to 89.8%,and combustion rate was increased from 2.25%/min to 3.15% /min. The additive also contains flux which help to induce liquid formation, such as calcium ferrite which has low melting point.Therefore, the formation rate of binding liquid was speeded at the lower sintering temperatures, and the volume of bond phase was also increased. Consequently, the yield and strength of sinter was enhanced largely. The industrial tests further demonstrated that the quality and productivity of sinter was improved dramatically after using sinter energy-saving additive.The unit productivity of sinter was increased by 15.72%, the tumble index by 1.99%, the solid fuel consumption decreased by 4.19 kg/t_sinter, the emissions of CO₂,CO,NO decreased by 10.53%, 35.29% and 25%, respectively .However, the average and peak concentration of SO₂ in the flue gas increased by 16.74% and 17.70%, respectively.The abatement of SO₂ emission is only achieved by desulphurizing the flue gas of sintering.Through the study of emissions of SO₂, NO_x, CO_x during iron ore sintering process, an integrated scheme of abatement emission of sintering flue gas was designed,which consists of the new technology of sectional desulphurization of the flue gas , sinter energy-saving additive and heat recovery from sintering and sinter cooling. Compared with the traditional FGD process, it is expected that the volume of flue gas can be reduced by 40%,and the investment of FGD equipment and operation costs can also be cut down by 40%. Recycling of part of the waste gas from the sinter strand can significantly save solid fuel consumption and bring direct economic profits of RMB9.36 million for 450m² sinter strand.更多还原